Synchronizing device for television systems



April 22, 1941. v P. DESERNO 2,238,932

SYNCHRQNIZING DEVICE FOR TELEVISION SYSTEMS Filed March 29, 1940 2 Sheets-Sheet 1 hie/7f: Peter 3656771 P. DESERNO April 22, 1941.

SYNCHRONIZING DEVICE FOR TELEVISION SYSTEMS Filed March 29, 1940 2 Sheets-Sheet 2 hkbfor:

FeZe'r Deserna Patented Apr. 22 1941 r UNITED STATES PATENT, OFFICE 2,238,932 smcnnomzmo DEVICE FOR. TELEVISION SYSTEMS Peter Deserno, Berlin, Germany, asslgnor to C, Lorenz Aktiengesellschaft, Berlin-Tempelhof,

Germany, a company Application March 29, 1940, Serial No. 326,566 In Germany March 18, 1939 i f 4 Claims. (01.178-695) complete picture will be transferred in & of a second.

As is well known, synchronizing impulses may be produced with the aid of discs provided with holes. It has been found, however, that the accuracy obtained in this way is far from sufiicient.

Another possibility resides in producing the pulsations electrically. The scanning line impulses may be obtained from the picture im pulses. To such end, the sinusoidal public mains frequency may be multiplied and, for instance,

the third or fifth harmonic filtered out therefrom and amplified. A second stage acts to filter one harmonic from the new frequency so obtained. By means of stages interconnected in cascade such multiplication may be continued so far that the scanning line frequency of 220.5X50=11025 hertz or cycles per second results from the mains frequency. The two pulsations so produced synchronize with each other. There is, however, no stable phase relation between them because any slight change in the form of the initial frequency causes the new frequency, derived therefrom by.

the said multiplication, to undergo a considerable phase displacement.

A method is known in which the picture impulse and the scanning line impulse are produced from an initial or main frequency by subdividing this. Such method, however, is useful to a certain extent only.

In order to explain this method reference is had to the schematic representation designated Fig, 1a in the accompanying drawings. The in vention is thereafter described with reference to Figs. 1a, 1b, 2 and 3, of which Fig. 1b is a graph illustrating the function of arrangements as provided by the invention, Fig. 2 is a circuit diagram that shows one embodiment thereof, while Fig. 3 is a graphical representation referred to in explaining the function of this embodiment.

As shown in Fig. 1a, also in this case stages H joined. in cascade are employed. Each stage serves to effect a subdivision of frequency in the ratio 1:7 or 1:3, for instance, and acts in a manner similar to the well known saw-tooth current generators or relaxation devices. The relaxation in each stage is started by the preceding stage. As in this way the starting point is precisely predetermined the frequency obtained by the described stepped reduction of frequency not only synchronizes with the initial frequency but also is independent thereof as regards phase.

The initial or main frequency in the case of interlaced scanning is double the scanning line frequency and according to the standard now in use is 441 times the picture frequency. This initial frequency, produced by a generator X, serves to control both a generator Y, employed for producing the scanning line impulses, and the next following lower frequency of the frequency-reducing cascade. The cascade may comprise four stages, for example, as shown in Fig. la, the two first stages effecting a subdivision of frequency in the ratio 1:7 while the subdivision caused by the two last stages is in the ratio 1:3.

This method requires the picture gap alternately to occur one time in company with the line gap and then accurately to occur in the middle of the line. By means of the said frequency reduction, starting from the initial frequency generator X and effected with the aid of relaxation generators, the picture impulse of a frequency generator Z will be coupled with the scanning line pulsations in a manner to be sufficiently stable in phase. However, the starting of the picture impulse does not in any case coincide with that of the line impulse. The detrimental phase shift B so incurred arises in the cascade through periods of losses which occur when synchronizing the stages thereof.

In order to overcome this drawback the invention proposes to construct the initial frequency generator X as an impulsing device for producing impulses whose width is regulable.

In Fig. ID, V denotes the up-s'lope or front flank" of the impulses produced by generator X, while R designates the down-slope or back flank. The flank V is used for synchronizing the first stage of the frequency-reducing c iscade, whereas flank R is to synchronize the line impulse generator Y. Y

The distance B between the flanks V, R is made to equal the phase shift that occurs in the cascade. For instance, distance B may be adjusted by varying a resistance. As in this case also the frequency of the generators is liable to quency remains constant despite varying the distance between V and R.

In the arrangement shown in Fig. 2 the initial frequency generator X and the line impulse generator Y are multi-vibrators of a known circuit connection. The I curves illustrating the grid and anode voltages are represented in Fig.

3. Ual and Ugl relate to the tubes I, I, of the two multi-vibrators, while U92 and UgZ refer to the tubes 2, 2. By means of the flank V of the impulse of Ug2 the first stage of the frequency-dividing cascade may be synchronized over C1. The same impulse when imparted over C2 to the grid of tube I" of the generator Y causes this generator to be controlled by means of flank R. The distance B between the flanks V, R is given by the magnitude of the elements Ck and Re of generator X. If for varying the distance B the resistance Rk is increased the curve E is flattened, as indicated by curve E. In conse-' quence of the fact that the rise of the grid voltage is delayed infthis way the period at the end of which the relaxation effect of the tube occurs is increased. As a result also the distance B is enlarged. At the same time the frequency of the,

amount B. By properly dimensioning the condensers Ck, Cg and Re, Rg the frequency and thedistance B will be adjusted in-a manner to compensate the phase displacement that arises within the cascade.

What is claimed is:

1. In an arrangement for generating synchronizing impulses in television systems for the production of a picture at a certain picture frequency and at a certain scanning line frequency, means for generating an initial frequency equal tosaid scanning line frequency or to a multiple thereof, a generator for producing this initial frequency, a generator for producing said scanning line frequency, a cascade comprising stages for reducing said initial frequency by subdivision in steps, and means under control of said initial frequency for imparting to the first of said cascade stages and to the said scanning line generator a phase shift adapted to compensate for a phase displacementdue to the said cascade.

2. In an arrangement according to claim l and means for producing by means of the initial frequency generator impulses the graphic representation of which has steep flanks, the trailing edge of said impulses being used to synchronize the line oscillator and the leading edge to synchronize the frame oscillator,

3. An arrangement according to claim 1, which comprises means for adjusting the width of impulses produced by the initial frequency generator.

4. An arrangement. according to. claim 1, wherein the initial frequency generator is adapted to produce impulses the graphic representation of which has-steep flanks, and. wherein means is employed for maintaining the frequency of this generator constant despite variation of the distance between said flanks.

PETER. DESERNO. 

